The invention relates to a method for regulating stable operation of an exhaust-gas turbocharger of an internal combustion engine. The invention also relates to an apparatus for carrying out such a method.
In certain operating states, especially when there is a torque demand, an internal combustion engine with an exhaust-gas turbocharger has phases in which there is an inadequate supply of compressed fresh air by the exhaust-gas turbocharger, giving rise to what is known as turbo lag. To eliminate this turbo lag, the increased air requirement is covered by a fresh-gas supply device by an additional fresh air supply, and the “transient performance” of the internal combustion engine is enhanced.
This additional fresh air can be taken from a compressed-air reservoir of a vehicle air system, for example. An increased air requirement can lead to adaptations to a compressor or air compressor supplying the compressed-air reservoir. In this case, pressure charging of the compressor can be performed, i.e. it receives charge air as inlet air downstream of the compressor of the exhaust-gas turbocharger in accordance with certain operating parameters of the internal combustion engine. In this way, it is possible to fully cover the increased air requirement.
The majority of compressors are mechanically driven, e.g. by the crankshaft of the internal combustion engine. Continuously pressure-charged compressors are also part of the prior art, especially in the USA.
Electronically regulated air-processing systems are likewise part of the prior art and are fitted as standard in commercial vehicles with air brakes. The electronic air-processing system contains a solenoid shutoff valve.
A fresh-gas supply device is known from WO2006/089779A1, for example.
All systems per se provide advantages in terms of fuel savings, emissions and/or the transient performance of a vehicle.
However, the operation of an exhaust-gas turbocharger may become unstable, something that may be caused by the occurrence of turbocharger “pumping” and is not prevented. Turbocharger pumping is caused by separation of the flow at the compressor blades. Separation of the flow occurs if a pumping limit is reached, i.e. in the case of certain relationships between the pressure conditions and the mass flow. In this respect, FIG. 1 shows a compressor characteristic map for a compressor of an exhaust-gas turbocharger. A throughput or mass flow is plotted on the abscissa, and a pressure ratio and delivery head of the enthalpy is plotted on the ordinate. In this case, families of characteristics are shown, of which the designation E is for characteristics at a constant speed n of the compressor. Characteristics E are plotted for six speeds n1 to n6, where n1>n6. Characteristics η1 to η4 with the same efficiency, where η1>η4, are furthermore indicated by the reference sign D. The point of intersection in a field of optimum efficiency η1 with a speed n3 and a characteristic F for surge-free inflow indicates a design point or operating point A. On the left hand side, i.e. toward low throughputs or mass flows, this family of characteristics is delimited with respect to an unstable range B by a pumping limit C.
Pumping causes high dynamic loads on the compressor blades and can lead to failure of the turbocharger.
During the air injection process by the fresh-gas supply device, the pumping limit C may be reached owing to a closed flap, which prevents the injected air from flowing back to the compressor of the turbocharger. This results from the fact that the turbocharger delivers the air downstream of the compressor against the closed flap. As a result, there is an ever decreasing mass flow and a simultaneous rise in the pressure ratio.
It is therefore the object of the invention to provide an improved method for regulating stable operation of an exhaust-gas turbocharger of an internal combustion engine.
One concept of the invention consists in regulating a stable range of an exhaust-gas turbocharger through the interaction of participating and already existing components of an internal combustion engine by switching over a compressor from a suction intake mode to a pressure-charged mode and back again on the basis of monitored operating parameters.
System behavior is thereby improved since an operating point of the exhaust-gas turbocharger remains in a stable range and does not enter an unstable range. In this way, turbocharger “pumping” is advantageously prevented.
Accordingly, a method for regulating stable operation of an exhaust-gas turbocharger of an internal combustion engine having a fresh-gas supply device, a switchover valve, a control device, a compressor and an air-processing unit with a discharge valve has the following method steps:
operating the compressor in a suction intake mode, wherein the switchover valve connects the compressor to an air inlet, and monitoring operating parameters of the internal combustion engine, of the air-processing unit and of the exhaust-gas turbocharger;
regulating stable operation of the exhaust-gas turbocharger on the basis of the monitored operating parameters by switching over the compressor from the suction intake mode to a pressure-charged mode, with the switchover valve connecting the compressor to a compressor of the exhaust-gas turbocharger; and
switching over the compressor on the basis of the monitored operating parameters from the pressure-charged mode into the suction intake mode, with the switchover valve connecting the compressor to the air inlet again.
With the aid of the switchover valve, which may also be termed an intelligent switchover valve, it is now possible to make a switch in the air system between a naturally aspirated mode of the compressor (taking the air from an air inlet ahead of the compressor of the exhaust-gas turbocharger) and a pressure-charged mode of the compressor (taking the compressed air after the compressor).
The control device determines the position of the switchover valve in accordance with various operating parameters, e.g. the engine speed and boost pressure.
Regulation can also involve monitoring a boost pressure and/or a mass flow of the compressor of the exhaust-gas turbocharger. In this case, the respectively current parameter determined is compared with a predeterminable limiting value, for example. If, for example, the boost pressure of the compressor nevertheless continues to rise, the outlet of the compressor can be connected to the atmosphere by opening the discharge valve. In a further embodiment, this can also be performed in stages or continuously, allowing particularly good adaptation to the respective operating state.
In the method step of regulation, operation of the fresh-gas supply device can form a monitored operating parameter. The switching-over of the compressor from the suction intake mode to the pressure-charged mode then takes place when the fresh-gas supply device is activated, and the switching-over of the compressor from the pressure-charged mode to the suction intake mode takes place after the fresh-gas supply device has been activated. These operating parameters are already available as signals, e.g. from an engine controller, and do not have to be additionally generated.
In the process of regulation, it is also possible for an overrun phase of the internal combustion engine and operation of the fresh-gas supply device to form monitored operating parameters. When the fresh-gas supply device is not in operation, the switching-over of the compressor from the suction intake mode to the pressure-charged mode takes place at the beginning of an overrun phase and the switching-over of the compressor from the pressure-charged mode to the suction intake mode takes place after the end of the overrun phase. In this way, the charge-air energy produced during the overrun phase is also used to produce and store compressed air.
It is also possible to eliminate a “waste gate valve” of an exhaust-gas turbocharger, if fitted therewith. In the method step of regulation, the operating parameters for operation of the waste gate valve of the exhaust-gas turbocharger in this case form monitored operating parameters, wherein a signal for opening the waste gate valve brings about the switching-over of the compressor from the suction intake mode to the pressure-charged mode and a signal for closing the waste gate valve brings about the switching-over of the compressor from the pressure-charged mode to the suction intake mode.
An apparatus for carrying out a method for regulating stable operation of an exhaust-gas turbocharger of an internal combustion engine has the following: a fresh-gas supply device for injecting additional air into the internal combustion engine when there is a requirement for transient power; a compressor for producing compressed air; and an air-processing unit for the compressed air, having a discharge valve. The apparatus is characterized by a switchover valve and a control device. The switchover valve connects the compressor to an air inlet in a suction intake mode of the compressor and connects the compressor to a compressor of the exhaust-gas turbocharger in a pressure-charged mode of the compressor. The control device is used to control the switchover valve for regulating stable operation of an exhaust-gas turbocharger.
The control device can also be designed to control the discharge valve, thereby making possible more appropriately tailored regulation of stable operation of the exhaust-gas turbocharger.
In one embodiment, the control device can be part of an engine controller or of the air-processing unit. Thus, no additional installation space is required.
In another embodiment, the fresh-gas supply device can have a throttle valve and an additional-air valve. If said valves and/or the discharge valve are valves that can be adjusted in stages or continuously, extensive further adaptation to specific operating conditions is possible.
The apparatus described is suitable for carrying out the method described above.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.